Method of sweetening oils



Patented Apr. 6, 1943 METHOD OF "SWEETENING OILS Vernon J. Loyd, East Chicago, Ind., assignor to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application July 31, 1941, Serial No. 404,835

4 Claims.

This invention has to do with the sweetening of petroleum hydrocarbons containing sour sulphur constituents, as mercaptans and the like, to render the material sweet to the doctor test.

In treating hydrocarbons, such as straight run gasoline, natural gasoline, cracked gasoline and the like, to render them sweet to the "doctor test,

the objective is to remove materials of the nature of dissolved sulphur, hydrogen sulphide, mercaptans or the like or to convert them to innocuous compounds. Washing with aqueous solutions of strong alkalies, such as caustic soda will remove most of the hydrogen sulphide and some, but not all. of the mercaptans. Washing with aqueous caustic to which some material has been added as a "solutizer, or solubility promoter, enables the caustic to dissolve and remove more or all of the mercaptans. Butylene glycols, butyric acids, and phenolic materials are so used. Older methods make use of sodium plumbite formed by dissolving lithage in caustic soda, the eiiect here being to convert mercaptan to mercaptides and I later to disulphides, which are innocuous to the doctor test, by addition of free sulphur.

In general, all processes of this kind leave something to be desired, and this field, one of the oldest in petroleum refining, is still the subject of active research,

The principal object of this invention is the provision of a novel process for rendering petroleum hydrocarbons sweet to the doctor test and reducing the amount of mercaptan sulphur.

This invention is based upon the discovery that efiective reduction of mercaptan sulphur may be eifected by treatment with aqueous caustic soda solution, containing tannic acid, in the presence of oxygen or an oxygen containing gas, such as air.

In this operation, the reaction is apparently not parallel to the usual solutizer type of operation, since the reaction apparently does not take place to any great extent in the absence of oxygen.

The caustic alkali solution to be used may be any of the usual alkaline solutions normally used for these purposes, such as caustic soda, caustic potash, alkali metal carbonates, ammonia and basic ammonium compounds and the like. Usual preference is had for caustic soda, in aqueous solutions of from about 5 Baum to 20 Baum, the usual and preferred strength being around 10 Baum.

The tannic acid used may be the usual commercial grade of the material.

We have found this tannic acid activator to be eflfective in quite small amounts, ranging from 5.0% downward to fractions of 1% with amounts of from about 0.3% to about 1.0% by weight of caustic solution being the most effective.

To avoid undue consumption of reagent it is best to caustic wash the oil, prior to this treatment, as with an aqueous alkaline reagent, to to remove hydrogen sulphide and the more readily removable sulphur containing materials.

The folowing experimental data show the efiectiveness'of the process herein described. To secure this data straight run and cracked gasolines were treated with various caustic alkali solutions, with and without tannic acid, in various concentrations, with oxygen present, with air, and with nitrogen to show the effect of oxygen elimination.

That: I

Eflect of tannic acid on removal of mercaptan sulphur from straight run gasoline by caustic solution [Raw 8. R. gasoline 0.005% RSH] Gas Number Mercap- NaOH Tanmc Temper- Ratio 0 atmosoi extan Kind B6 acid ature (N aOH.Gaso.) phem "actions removal Per cent F. Per cent 0. 3 100 1:4 All--- l 72. 5 1.0 100 1:4 A112--- 1 a 72. b 5. 0 100 1:4 Lin--- 1 07. 5 0. 0 100 1:4 AIL--. l 25. 0 1. 0 82 1:4 A111--- 3 75. 0 0.0 1:4 NI.-. 1 29.0 0. 0 90 1:4 01.... l 20. 0 1.0 90 1:4 Nu-.- 1 31.8 1. 0 90 1:4 0|..... 1 73. 4 5. 0 90 1:4 01..... 1 02- 5 mm. II

E'fiect of tannic acid on removal of mercaptan sulphur from cracked gasoline by caustic solotion [Thermal cracked gasoline 0.025%ZRSH1 Gas Number Merm NaOH kind Tannin Temper- Rat1o atmos ofex A? tan B. ac1d ature (NaOH.Gaso.) phere actions whom Per cent F. Per cent Fres'n10.3 0.0 100 114 A112... 1 5 Do 0:3 100 1.4 1111-... 1 D 1.0 100 1.4 1411.... 1 31,g Regeneration l 7 (epprox.) 0.0 95 1:4 1 60,2 Regeneration 1 NaOH solu. boiled before using. with).

The above data demonstrate the effectiveness 3. That method of removing mercaptans from of the reagent. gasoline and the like comprising contacting the I claim: 35 oil in the presence of oxygen-with an aqueous 1. That method of removing mercaptans from solution of caustic soda activated by the addition petroleum fractions comprising contacting the of a small amount, less than about 5%, of tannic fraction with an aqueous alkaline reagent to acid. which tannic acid has been added, in the pres- 4. That method of removing mercaptans from ence of oxygen. 40 gasoline and the like comprising contacting the 2. That method of removing mercaptans from gasoline and the like comprising contacting the oil in the presence of oxygen with an aqueous solution of caustic soda activated by the addition of a small amount of tannic acid.

oil in the presence of oxygen with an aqueous solution of caustic soda activated by the addition of a small amount, from about 0.3% to about 1.0%, of tannic acid.

VERNON J. LOYD. 

